Isolation of mutants Pigmented and nonpigmented mutants Antibiotic-resistant mutants within the inhibition zone · Genetic marker, such as the expression ofβ- galactosidase that produces the blue colorIsolation of Mutants • Pigmented and nonpigmented mutants • Antibiotic-resistant mutants within the inhibition zone • Genetic marker, such as the expression of b￾galactosidase that produces the blue color